fprintf 不工作 [英] fprintf not working

问题描述

我正在测试 fprintf() 的用法，但它不起作用.当我第一次编写代码时，我忘记在 fprintf() 中添加 并且它起作用了.但是，当我在test 1 2"开始时添加 时，它停止工作.

#include #include int主(){FILE* f = fopen("test.txt", "r+");if( f == NULL) 返回 0;字符 str[4][10];for(int a = 0; a <= 3; ++a){fscanf(f, " %[^	
]s", str[a]);printf("%s
", str[a]);}fprintf(f, "
test 1 2
");fclose(f);系统(暂停")；返回0；}

并且我的 test.txt 包含(而不是 和 我按 Tab 键并输入文件，但我无法在这里管理它)<块引用>

a b c d e fg

解决方案

对于为追加而打开的文件(包含+"号的文件)，在允许输入和输出操作，流应该被刷新 (fflush) 或重新定位 (fseek, fsetpos, rewind)要么是写操作，然后是读操作，要么是未到达文件末尾的读取操作后跟写操作.

来源

所以添加这个:

fflush(f);

在你的 fprintf 之前，如果你想附加到文件而不删除它以前的内容，或者这个:

rewind(f);

如果你想覆盖你评论中指出的内容.

I'm testing the usage of fprintf() and it is not working. When I first wrote the code I forgot to add inside fprintf() and it worked. However, when I added at the start of "test 1 2" it stopped working.

#include <stdio.h>
#include <stdlib.h>

int main ()
{
    FILE* f = fopen("test.txt", "r+");
    if( f == NULL) return 0;

    char str[4][10];

    for(int a = 0; a <= 3; ++a)
    {
        fscanf(f, " %[^	
]s", str[a]);
        printf("%s
", str[a]);
    }

    fprintf(f, "
test 1 2
");

    fclose(f);
    system("pause");
    return 0;
}

and my test.txt contains ( instead of and I pressed tab and enter in the file but I couldn't manage it here)

a b c d e f g

解决方案

For files open for appending (those which include a "+" sign), on which both input and output operations are allowed, the stream should be flushed (fflush) or repositioned (fseek, fsetpos, rewind) between either a writing operation followed by a reading operation or a reading operation which did not reach the end-of-file followed by a writing operation.

Source

So add this:

fflush(f);

before your fprintf if you want to append to the file without deleting its previous contents, or this:

rewind(f);

if you want to overwrite the content, as pointed by your comment.

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